In the production of devices for micro/nano technologies, there is a great demand for non-invasive sensors for monitoring the deposition of thickness of a film on a substrate. The substrate can, for example, be a silicon wafer.
Various types of sensors are known in the micro/nano scale fabrication arts. For example, there have been several types of optical fiber sensors reported in the technical literature for sensing different physical properties. These types includes fiber optic temperature sensors with ultra-thin silicon etalon, glucose monitoring using fluorescent microspheres, various applications with Whispering Gallery Modes (WGM) resonators, bimetallic optical temperature sensors, acceleration sensors using microsphere resonators, and optical fiber pressure sensors. Each of these reported fiber optic sensors has its own advantages and disadvantages.
The aforementioned reported fiber optic sensors have various types of sensing capabilities and qualities. However, these have not found widespread industrial application due to their design complexity and high production costs, or because they may be invasive for a given application.
The quality of integrated circuit (IC) and micro-electro-mechanical system (MEMS) devices are mostly depend on efficient control of thin film deposition upon a substrate. Device performance and characteristics are gradually improving as active research is applied to thin film deposition and more accurate monitoring of the film thickness. Such monitoring includes direct optical monitoring of thickness and refractive index, an end-point detector for parylene deposition, an optical fiber sensor to monitor polymer growth, optical monitoring of thin-film deposition, optical monitoring of thin-films with spectroscopic ellipsometry, and an evanescent wave sensor to monitor the deposition rate of thin-films. However, efficient monitoring of thin film deposition rate and thickness are still a great challenge in thin film industries.
There is accordingly a demand for optical sensor technology for monitoring thin film deposition, which is non-invasive, relatively easy to fabricate, relatively easy to use, and having relatively low production costs.